1. Field of the Invention
The present invention relates to a process for producing colloidal crystals immobilized with a polymer and colloidal crystals immobilized with a polymer.
2. Related Background Art
It is known that colloidal crystals having an ordered structure composed of colloidal particles reflects a light having a wavelength corresponding to the lattice constant of the colloidal crystals due to Bragg diffraction. For example, colloidal crystals composed of three-dimensionally ordered submicron colloidal particles reflects a light having a wavelength in a range from ultraviolet light and visible light to infrared light It is known that, when such a colloidal crystal reflects visible light, so-called structural color, such as iridescence (iris color), can be observed. Due to the characteristics, such colloidal crystals are expected to be used in various applications, such as a color material exhibiting structural color, an optical filter impermeable to a light having a certain wavelength, a mirror reflecting a certain light, a photonic crystal, an optical switch, and an optical sensor. Thus, various colloidal crystals and the process for producing those have been investigated.
For example, Japanese Unexamined Patent Application Publication No. Hei 6-100432 (JP 6-100432 A) discloses that colloidal crystals can be obtained by removing contaminating ions (cations and anions) from a particle dispersion having water or a water-organic solvent as a dispersed medium in order to highly deionize the solution. The Japanese Unexamined Patent Application Publication No. Hei 11-319539 (JP 11-319539 A) discloses a process for producing colloidal crystals. In the process, a weak electrolyte, which changes its dissociation degree in the liquid medium according to temperature variation, is added to a colloidal dispersion system in which colloidal particles each charged on the surface are dispersed in the liquid medium, and the colloidal dispersion system is externally heated or cooled so that the colloidal particles are arranged. Moreover, Japanese Unexamined Patent Application Publication No. 2002-28471 (JP 2002-28471 A) discloses a process for producing colloidal crystals. In the process, shear flow is applied to a monodispersed particle suspension in a colloidal crystal state to cause the monodispersed particle suspension to flow, in a space between two smooth substrate surfaces facing in parallel with each other, in a single axis direction parallel to the substrate surfaces. Thereafter, the monodispersed particle suspension is kept stationary to allow colloidal crystals to form. Japanese Unexamined Patent Application Publication No. 2002-128600 (JP 2002-128600 A) also discloses a process for producing colloidal crystals in which colloidal crystals are formed from crystals appeared in a colloidal suspension by applying, to the crystals, oscillation having an acceleration in a range from 0.1 G to 10 G and/or stress oscillation of 20 Pa or higher to allow the crystals to grow to a certain size. Furthermore, International Publication No. WO2005/045478 (WO 2005-045478 A) also discloses a process for producing colloidal crystals in which particles are added to monomer comprising ethoxylated trimethylolpropane triacrylate (ETPTA), and then the resultant mixture is spin-coated and immobilized to obtain the colloidal crystals.
However, it is difficult to control the structure (the lattice constant, the crystal type) of the colloidal crystals obtained by using the a process for producing colloidal crystals disclosed in JP 6-100432 A, JP 11-319539 A, JP 2002-28471 A, and JP 2002-128600 A. For example, the colloidal crystals obtained as described above essentially need to be immobilized in order for them to be used in practical application as various materials, such as a color material exhibiting structural color, an optical filter, a mirror, and a photonic crystal. However, when the colloidal crystals are immobilized after drying, the crystal structure of those is turned into a closed packing structure; thus, in the process, it was not able to control so that the structure of such colloidal crystals may turn into another structure. For this reason, it was difficult to use the conventional immobilized colloidal crystals described in JP 6-100432 A, JP 11-319539 A, JP 2002-28471 A, and JP 2002-128600 A in practical application such as optical materials. Meanwhile, there is another immobilization method in which colloidal crystals formed in a liquid are immobilized by a polymer gel to obtain a colloidal crystal gel. A problem involved in such a method is that the colloidal crystals are destroyed or a crystal structure is distorted and changed due to evaporation of a solvent in the process of immobilization. As for the conventional process for producing colloidal crystal described in WO 2005-045478 A, colloidal crystals formed in a liquid are directly immobilized with polymers. In the process, although colloidal crystals can be immobilized in the state of including no solvent (not in a gel), it is considered to be necessary to go through a spin-coating process in order to form an ordered array of the colloidal particles. Accordingly, it is difficult to apply the process for various purposes.